Who hasn't seen a lost child, with tear-stained cheeks, wandering at an amusement park or airport?

Parents might feel less anxious with a product called Safetytat (www.safetytat.com), a temporary, stick-on tattoo on which you can write a phone number. They come six to a pack, with a marker (about $10). Or they are sold customized, with warnings about allergies or other information (about $20 for 24).

The package suggests that caregivers write a cellphone number on the tattoo and don't include the child's name. The tattoos are waterproof.